1. Field of the Invention
The present invention is directed to an implantable defibrillator arrangement, and in particular such an arrangement making use of a capacitor and an inductance for generating an electrical defibrillation pulse.
2. Description of the Prior Art
In implantable defibrillator arrangments, as exemplified by U.S. Pat. No. 4,834,100, it is conventional to provide a capacitor in an implantable housing, the capacitor being connectable for charging to a voltage source in the housing via a controllable switch arrangement, and also being connectable through an inductance to electrodes arranged in the region of the heart, by means of electrode leads, for generating an electrical defibrillation pulse and supplying the pulse to the heart tissue. In the arrangement disclosed in U.S. Pat. No. 4,834,100, the capacitor is connectable through a controllable switch arrangement either to a voltage source or, in series with an inductance, to two electrode terminals. Electrode leads are connectable outside of the capsule housing to the terminals, the leads terminating in electrodes which are placed at or in the heart of a patient. The capacitor is charged to a prescribed charging voltage as long as the capacitor is connected to the voltage source. For releasing an electrical defibrillation pulse to the heart, the capacitor is briefly connected, via the inductance, to the electrodes by means of switch arrangement, causing a biphase current pulse in the form of a highly attenuated oscillation to be generated. Such a pulse shape has proven particularly effective with respect to the energy required for defibrillation.
The shape of the oscillation is defined by the values of the capacitance of the capacitor, the inductance, and the electrical impedance of the heart tissue between the electrodes. This electrical impedance is substantially dependent on the particular type of electrodes employed, including their shape and their positioning relative to the heart. The defibrillation pulse supplied by this known defibrillator system can therefore significantly deviate from a waveform which is considered optimum, dependent upon which electrodes are employed and on the positions of the electrodes.